Add configuration for git

- Add .config/git/config
  + Define aliases
  + Configure default behavior in various situations
  + Add user information with signing key
- Add .config/git/commit_msg_template.txt
- Add .config/git/ignore
- Integrate `git` aliases into the shell

.config/shell/aliases

@@ -3,9 +3,6 @@
 # Aliases used in all kinds of shells
 
 
-# Manage the bare `git` repository in ~/ holding the dotfiles
-alias dotfiles='git --git-dir=$DOTFILES_DIR --work-tree=$HOME'
-
 
 
 forget() {  # the current history and restore $HISTFILE from disk
@@ -72,3 +69,31 @@ alias la='ls --classify --format=vertical --almost-all'
 alias lal='ls --classify --format=long --almost-all'
 alias ll='ls --classify --format=long'
 alias lla='lal'
+
+
+
+if _command_exists git; then
+
+    # Manage the bare `git` repository in ~/ holding the dotfiles
+    alias dotfiles='git --git-dir=$DOTFILES_DIR --work-tree=$HOME'
+
+    alias g='git'
+
+    # Create "g" prefixed aliases from the "real" aliases
+    # defined under "[alias]" in ~/.config/git/config,
+    # for example, `gap` for `git add --patch`
+    #
+    # Interactive shells only: This spawns a `git` process,
+    # which every non-interactive `bash` via `$BASH_ENV`
+    # (e.g., ":!cmd" in `vi`) would pay on each command
+    # => There, `g ap` works just as well as `gap`
+    case $- in
+        *i*)
+            for al in $(git aliases --real); do
+                eval "alias g$al='git $al'"
+            done
+            unset al
+            ;;
+    esac
+
+fi